The present invention relates to a ceramic material based on tricalcium phosphate Ca.sub.3 (PO.sub.4).sub.2 doped with a limited amount of zinc. More particularly, the invention relates to a ceramic body containing tricalcium phosphate doped with zinc suitable as a surgical implant for a hard-tissue of a living body.
As is known, several ceramic materials are officially approved for use as a surgical implant for hard-tissue in the living body including alumina, hydroxyapatite, tricalcium phosphate, AW-glass ceramic, carbon and the like. A ceramic material for a surgical implant has no pharmaceutical effect to promote bone formation, to inhibit bone resorption, or to promote tissue restoration. Therefore, it is necessary for a patient to be administered with some supplemental medicines in addition to the surgical implants in order to promote bone formation, to inhibit bone resorption, or to promote tissue restoration. It is desirable that a surgical implant in itself may have such pharmaceutical effects.
On the other hand, zinc is known to have the above mentioned pharmaceutical effects when taken into a living body in a limited dose although toxicity appears by a large amount of zinc dose. Accordingly, zinc-containing ceramic materials are proposed for use as a bone substitute material including those consisting of 10 to 50% by weight of ZnO, 30 to 40% by weight of CaO and 10 to 40% by weight of P.sub.2 O.sub.5 and those consisting of 10 to 50% by weight of ZnSO.sub.4, 30 to 40% by weight of CaO and 10 to 40% by weight of P.sub.2 O.sub.5 (see U.S. Pat. No. 4,778,471) and those consisting of 7% by weight of ZnO, 25% by weight of CaO and 68% by weight of P.sub.2 O.sub.5 (see U.S. Pat. No. 4,376,168). These zinc-containing ceramic materials, however, are considered not to be quite satisfactory as a bone substitute with the pharmaceutical effects because the ceramic materials contain, besides the phases of tricalcium phosphate and hydroxyapatite, several other phases having lower biocompatibility or safety to a living body. This is because they contain a relatively large amount of zinc. No animal tests undertaken with these zinc-containing ceramic materials demonstrated the above mentioned pharmaceutical effects.
Further, it is known that a ceramic body consisting of the phases of tricalcium phosphate and/or hydroxyapatite has the best biocompatibility with hard tissues. When such a ceramic body is implanted in a bone, direct connection is formed between the bone and the ceramic body without intervention of any fibrous connective tissues. Accordingly, it is desired to develop a hard-tissue substitute having both the above mentioned pharmaceutical effects and high biocompatibility. Extensive investigations have been undertaken therefore to obtain a zinc-doped ceramic material consisting of the phase of tricalcium phosphate, optionally, in combination with the phase of hydroxyapatite exhibiting high biocompatibility and capable of promoting bone formation by releasing zinc within a living body.